The invention relates to a stitcher and a method for stitching strips of rubber material together into a substantially continuous strip.
For manufacturing for instance an unvulcanized tyre or air spring with components of rubber material, use is often made of one or more strips of rubber material that have to be stitched together. In that case the stitch is placed at an acute angle to the longitudinal direction of the strips so that the stitch will extend at least partially over the circumference of the unvulcanized tyre or air spring.
When manufacturing an unvulcanized tyre or air spring use is also made of one of more strips of a cord-reinforced rubber material. In that case the reinforcement cords need to be placed at an angle α to the longitudinal direction of the strip. As basic material for the manufacturing of the substantially continuous strip, use is made of a roll of rubber material, in which reinforcement cords have been embedded in the longitudinal direction. The cords embedded in the rubber material may for instance be of steel, rayon or a synthetic material, such as nylon, polyester or aramid, or the like. In a cutting system strips of cord-reinforced rubber material are cut one by one at an angle, the cutting angle α, from the roll of rubber material. As a result the strips in general have the shape of a parallelogram, having a substantially triangular leading tip en a substantially triangular trailing tip. The individual strips are transported one after the other by a supply device to a stitcher, after which the edges of two consecutive strips of cord-reinforce rubber material are stitched together, preferably by means of butt stitching or butt splicing, into a substantially continuous strip of cord-reinforced rubber material, wherein the reinforcement cords and the longitudinal direction of the continuous strip substantially include an angle α.
In case of butt stitching the strips of in general sticky unvulcanized rubber material are pressed against each other and for instance a stitching roller is moved over the stitch so that the strips will start to form one unity. The outer ends of the strips are placed butt against each other, substantially without overlap.
A device for manufacturing such a substantially continuous strip of rubber material in this way is for instance known from European patent publication 0 698 479 A1. In this document a stitcher is described having a stitching head with stitch unit placed over the stitch table, wherein the stitching head is movable along a straight guide or rail, defining a stitch line, wherein the stitch line and the longitudinal direction of the continuous strip include an angle α. The guide or rail is placed over the stitch table so as to be slightly rotatable, so that aligning the stitching head with respect to the edges of the strips to be stitched is possible.
A drawback of said known device is that the angle α to be set is limited, as a result of which the device is unsuitable for manufacturing different substantially continuous strips of for instance cord-reinforced rubber material having a wide range of angles α to be set between the reinforcement cords and the longitudinal direction of the continuous strip.
This problem could for instance be solved by increasing the angle of rotation over which the guide or rail can be rotated. However, for obtaining a larger angle of rotation, particularly for obtaining smaller angles α, the rail should be much longer than the continuous strips are wide. For accurate stitching with such a long rail, a firm and therefore heavy structure is required in order to counteract the possibility of the rail sagging.